A color picture is generally made of three color components R, G and B. These components are generally correlated, and it is very common in image and video compression to decorrelate the color components prior to processing the pictures. To that purpose, the most common format used is the YUV color format (or another similar variant called YCbCr). YUV signals are typically created from RGB pictures, by using a linear transform of the three inputs R, G and B. In the YUV format, U and V are second color components and Y is the first color component. The three components are currently considered as color components.
The image or picture and in particular its color components are associated with quantization parameters QP (typically between 0 and 51) used in the quantization process of coefficients derived from pixel sample values by a transform (for instance the DCT or the DST), during the image encoding and in the dequantization process during the image encoding and decoding.
In the video standard HEVC, for example, there is a link between the quantization parameters QP applied to the first color component (which is the first color component in case of YUV color format, and can be for instance the G color component in case of RGB color format), hereafter denoted QPY, and the quantization parameters QP applied to the other color components called second color components (which are the second color components in case of YUV color format, and can be for instance the R and B color components in case of RGB color format), hereafter denoted QPC.
To generate QPC from QPY, an intermediate value QPI is calculated as follows:QPI=MAX(−QPBdOffsetC,MIN(57,QPY+QPOffsetC))
Wherein:                QPBdOffsetC is a pre-defined offset depending on the bit-depth used to represent the second color component, and        QPOffsetC is an offset that enables to partly control the link between QPY and QPC.        
Then, the quantization parameter applied to the second component QPC is derived from the intermediate value QPI using for example one of the following correspondence tables (from the current draft of the Range Extension of HEVC) selected depending on the used color format (specified by a parameter ChromaArrayType):
TABLE 14:2:0 YUV color formatChromaArrayType = 1QPI<303031323334353637383940414243>43(4:2:0 YUVQPC=QPI2930313233333434353536363737=QPI − 6color format)
TABLE 24:2:2 YUV color formatChromaArrayType = 2QPI<3333 ≤ QPI < 39394041424344454647484950>50(4:2:2 YUVQPC=QPI=(QPI − 1)373839404041424243444445=QPI − 6color format)
TABLE 34:4:4 YUV color formatChromaArrayType = 3 (4:4:4 YUV color format)QPI<51≥51QPC=QPI51
Thus, these tables are used to obtain the quantization parameters of the second color component, each time in correlation with the color format used. In the first version of HEVC (the version issued before the Range Extension version), only the Table 1 is specified and used. In the current draft of Range Extension specification, the two additional tables (Table 2 and Table 3) have been added.
Even if they allow a generalization to several color formats, of the first version of the HEVC standard which was focused on the 4:2:0 YUV color format, there is no flexibility in the choice of the table since to one color format is associated one and a single table.
Furthermore, in order to allow the generalization of HEVC standard to the other color formats than 4:2:0 YUV, additional memory is required to store the values of Tables 2 and 3.